1. Field of the Invention
The invention relates to a collection container assembly that includes a plurality of nested containers formed from different respective materials and provides an effective barrier against water and gas permeability and for extending the shelf-life of assembly.
2. Description of the Related Art
Plastic tubes have an inherent permeability to water transport due to the physical properties of the plastic materials used to manufacture the tubes. Therefore, it is difficult to maintain the shelf-life of plastic tubes that contain a liquid additive. It is also appreciated that deterioration of the volume and concentration of the liquid additive may interfere with the intended use of the tube.
In addition, plastic tubes that are used for blood collection require certain performance standards to be acceptable for use in medical applications. Such performance standards include the ability to maintain greater than about 90% original draw volume over a one-year period, to be radiation sterilizable and to be non-interfering in tests and analysis.
Therefore, a need exists to improve the barrier properties of articles made of polymers and in particular plastic blood collection tubes wherein certain performance standards would be met and the article would be effective and usable in medical applications. In addition, a need exists to preserve the shelf-life of containers that contain liquid additives. The time period for maintaining the shelf-life is from manufacturing, through transport and until the container is actually used.
Some prior art containers are formed as an assembly of two or more nested containers. The nested containers are formed from different respective materials, each of which is selected in view of its own unique characteristics. Some nestable containers are dimensioned to fit closely with one another. Containers intended for such assemblies necessarily require close dimensional tolerances. Furthermore, air trapped between the two closely fitting nestable containers can complicate or prevent complete nesting. Some prior art container assemblies have longitudinal grooves along the length of the outer surface of the inner container and/or along the length of inner surface of the outer container. The grooves permit air to escape during assembly of the containers. However, the grooves complicate the respective structures and the grooved containers still require close dimensional tolerances.
Other container assemblies are dimensioned to provide a substantially uniform space at all locations between nested inner and outer containers. Air can escape from the space between the dimensionally different containers as the containers are being nested. Thus, assembly of the nestable containers is greatly facilitated. Additionally, the nestable containers do not require close dimensional tolerances. However, the space between the inner and outer containers retains a small amount of air and the air may be compressed slightly during final stages of nesting. Some such container assemblies are intended to be evacuated specimen collection containers. These container assemblies are required to maintain a vacuum after extended periods in storage. However, air in the space between the inner and outer containers is at a higher pressure than the substantial vacuum in the evacuated container assembly. This pressure differential will cause the air in the space between the inner and outer containers to migrate through the plastic wall of the inner container and into the initially evacuated space of the inner container. Hence, the effectiveness of the vacuum in the container assembly will be decreased significantly. These problems can be overcome by creating a pressure differential between the annular space and the inside of the inner container to cause a migration of air through the walls of the inner container. The inner container then is evacuated and sealed. This approach, however, complicates and lengthens an otherwise efficient manufacturing cycle.